Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The outer broken lines in the FIGURE show a display screen or portion thereof and the broken lines in the FIGURE show portions of the graphical user interface; the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 